In the quietened boardroom, three great minds are in hushed conversation, their greying heads tipped together. Sir Alan Sugar and his two sidekicks are puzzled by the Jewish candidate who didn't know what a kosher chicken was.

"But he's clever, isn't he? Didn't he go to Edinburgh?" says one, Nick Hewer. "Well," weighs in the only woman in the room, and with a slight sneer. "I think Edinburgh isn't what it used to be."

And with eight words, a city fell. Well, not quite fell, but certainly wondered what it had done to incur the wrath of Margaret Mountford.

The eminent Mountford is, to the outside eye, a bit-part player in the tremendously successful series The Apprentice. A formidable force in British business, she was born in Northern Ireland and read law at Girton College, Cambridge. Late in her career, she has found a fame she never expected as the UK's favourite disapproving headmistress. As one of the two aides to Surallun, she shadows the teams on their tasks, delivers the results to the boss and helps to decide who should stay and who be fired.

Clearly, then, a powerful, public figure. Will Edinburgh University be burning the library down, hanging up its mortar boards and calling it a day? "The University of Edinburgh is one of the UK's most successful and popular universities," replies a spokesman, by email. "It is regularly ranked among the top 50 universities in the world and is currently going through a period of unprecedented growth."

He would not be drawn further into a discussion on the devastating effect Mountford might have on future university statistics. But her withering putdown shows how integral she has become in a show watched by millions every week. As each series develops, the interplay between Surallun and his aides - who have both been working with the Amstrad overlord on normal, non-televised business projects for more than 20 years - has a kind of magic that no television producer could have been expecting.

The interplay between Hewer, Mountford and the contestants, meanwhile, often feels like a couple of university professors asked to teach a nursery-school class - or a pair of curious children given free rein to examine the scuttling of some tiny insects with a magnifying glass on a sunny day.

While the candidates themselves beetle about performing their ludicrous tasks, the camera cuts to Mountford or Hewer providing a perfect reflection of whatever the audience happens to be thinking - whether it's an approving nod or a stare so fearsome you wonder that the victim doesn't burst into flames.

Mountford's signature look is the rolling of her eyes to heaven. Indeed, most of her loudest comments about the candidates are almost entirely nonverbal. The eye-rolling is frequently accompanied by a heartfelt sigh; in extremis, a sickened pursing of the lips. Her reaction to any act of stupidity is to drop her jaw in shock and amazement. Complete idiocy causes an additional flaring of the nostrils.

As contestant Michael Sophocles celebrated his team's Singles' Day greetings cards having won the task - by dint of being the "least worst" product on offer - with whoops, shouts and air-punching, Mountford could not have looked more disgusted had he marched an army of water buffalo into the boardroom and asked them all to fart on cue.

But it's also Mountford's quick-witted plain-speaking nature that we love. Outside a pub, avoiding Sophocles' appalling Frank Sinatra impressions at his team's Italian-themed evening, she commented: "I'm not sure what has more cheese in it, the pizza or that racket."

When high-cheek-boned but responsibility-shy Alex tried to avoid claims of having stepped back when asked to be deputy leader, scared of being blamed later, Margaret told the boss, and the world, with a snort: "You stepped so far back from it you were practically out the room."

You wonder how long her patience can last. As she heaves yet another sigh and drops her shoulders another weary inch, it seems unlikely that she would want to sign up for another series where her beloved world of high business is turned into a circus of shiny suits.

However, the loss of Mountford would be a terrible blow to the series. She is our voice on screen, our bridge between the unbearable back-stabbing candidates and the real world. Without her, would we still make the leap?